Radio tuning arrangement



Oct. 21, 1941, w; J. POLYDOROFF 2,260,088.

RADIO TUNING ARRANGEMENT Filed June 19, 1959 s Sheets-Sheet 1 Oct. 21, 1941. w. J. POLYDOROF-F- 2,260,088

RADIO TUNING ARRANGEMENT Filed June 19, 1939 5 Sheets-Sheet 2 Q I K/LOICYICILES 5'50 abo 53'0 76a 7.5-0 500 @QCQCQ w. J. POLYD OROFF RADIO TUNING ARRANGEMENT Oct. 21, 1941.

FiledJune 19, 1939 3 Sheets-Sheet 5 FIG. 7

AVG

Patented Oct. 21, 1941 I UNITED STATES PATENT OFFIQE 2,260,088 sn re mm minimalismwlaaima' J2 iwmierdshw liiiett', I11.- strait-mane 19, 1939, see-a1 NI). 279,894 In Great Britain July 12, 1-938 3 claims. (o1'.250'-'--40) relates tuning arranghmelits tinuoustuning of said circuits. The invention provides novel and convenient tuning and switching means whic have ereat convenience ofhq r on ..t seti.1. rv with a olishing'oi usually employed tuning means.

It is already known how to operate a radio receiver in a, manner such that several preferred stations in the broadcast range can be brought in by a push buttonmechanism'. Such existing systems either employ complicated mechanical selector, devices operating on the tuning controls, ora plurality of electrically pre-set groups of circuits, each group'responsiveto thefrequency of a desired'station. The first described system lacks the requiredyprecision when the" tuning. mechanism is directly operated .by mechanical means, and in order to. increase the accuracy; costly electric motors are often employed. The second system requires duplication of-jfltun'ihg equipment in order to also provide continuous tuning. The choice of ,preeset stations varies with localities. This is particularly important-in mobile receiversiautomobile or portable). and a frequentre-adjustment of stationsettings may be required, the mechanism for which in present systems is not readily accessible to the .operat'orl Unless a complicated automatic frequency'con- U'Dlxcircuit' is employed; in the: receiver these- Pro-settings may require correctiori, as the re-'- ceiver may drift in frequency with tempe'rature and power fluctuations, otherwise de-tuning anddistortion occur.

Thepresent invention describes .a new and improved tuning arrangement and method-- of tuning in which the above describeddefe'ct's are eliminated. The invention is applicable to oilc;uits .tuned by either variable inductance or variable capacity or' both of such types in which a rotation of a knob produces the changes of electrical quantity, governing the frequency 'a'd justment and Which'ca'n be easily calibrated; To this type belong inductances tunable by magnet core, movable linearly or rotating in a semispherical winding, revolving coils with sliding contact and rotary condensers having two eeri centric caps closing. the gap and movable short circuiting ring. I

The main object of the inventionisto provide a compact andreadily adjustable ar angement of tuning parts which permit' the selection of preiset; stations as well as continuous tuning, without the employment of the usual variable condenser orinductance units 'ga'nged together. Another object is to provide a-convenientand novel tuning indicator: m connection 'withfthel ad'iustable cir'cuits which enables th operator to instantaneously selector change at will the desired stations by .s ,imple means, r Still another object is; to provide. anarrangemerit of,.-e,1ectrical circuits and their constants'so as to derive, the benefits: ofthe. invention? inv several; possible. applicationsof the: system tovarious frequency bands encountered in a radio receiver. l .T inve t-ionwill be, better understooddf reference is made-to the accompanying drawings" inwhichg, r Fi Sh ws one sectionof the. tuning unit;

Fig, 2 shows amodification O'Lthis .unit.1

,Fig. 3 is the front view. of oneo'f the-above units with its dialing indicator, and Figure4 its modification. Figs. 5,1 6, and ..7f show the electrical circuit arrangements. According to the inventiomreach present conventional, frequency band.- of. the re-I ceiver is subdivided into: severalQpart-ranges; which; subera-nges may be. in duplicate, andtare continuously tunable. either in: every separate circuit-or by having'certain circuits permanently adjustedto respond to. the whole part-range;

, Accordingly; the. tuning ratio -.(ratio of: LC oi-each tunable circuit) is;considerablycreduced' and; a band; spread is obtained; This ispar; ticularly needed, in short wave tuning", where a crowding; of stations 1 occurs over certain small regions of the entire .short wave. band. The following example illustratesuthe normal and novel tuning ratio requirementszp,

The, conventional broadcastqbandlused this" country at the presenttime normally requires 'a tuning ratio of-j8.5 in orderto cover the band-"of frequencies from 540-to 1560 kc. 1

This band may be divided into. three" partpact design. which will answer the requirementsof reduced tuning ratio. It is also commented make the mechanism selecting the desired par -j range and its tunable circuits into" one unit,

which essentially willconsist of a push button operated" switch; assembled with its circuits, tuning elements and the dial indicator I means."

In, order to'isave' on partsandspace'the samev .op'eratingparts may perform the two functions of tuningand sele'ctingth ranges.

.celling any previous connections made.

Fig. 1 shows one such arrangement of the new tuning device. A push-button switch is represented by I. The switch may be made of several sections, depending on how many sub-ranges and station selectors are required. Thus in the above example of subdivision of the broadcast range into three ranges, it may be desirable to have two pre-set or tunable channels in each sub-range range, subdivided into three ranges of which two ranges have duplicate tuning to enable to "preset two stations in one sub-range and three short-wave ranges, which, for example, may be selected as follows: first 6-7 mc.; second 9.5-12 me. and the third 15- 8 mc., which subdivision practically takes care of all the world distribuin which case a six section switch will be used.

If, in addition, three or four short wave .spreadtuned sub-ranges will be used'the switch will contain 8 to 10 sections. Theblade -2 of-the switch when pushed inwards closes the circuitconnections of the section at the same time can- The switch blade isbentat the right angle and a knob 3 inserted at. the end pushes the blade in, while the. knob. may at the same time be rotated. -A channel 4. is'fixed to the switch body andcmayserve for the coilassembly as well as for the tuning mechanism. jA coil 5, having a winding .6 and a threadedbushing 'I is arranged to move along its axis, when screw 8 is-rotated. The rotation of coil is prevented by guide pins 9. Screw .8 is centered in the channel 4 and terminates with a pinion IE9 gradually reducing in tooth height toward the knob. The knobhas a hollow shaft II. of such form as to engage with the pinion I when completely pressed against the pinion. When the switch is open the pinion is dis-engaged. r

(The movement to the right closes the switch and simultaneously or with further pressing the pinion is engaged'so that the rotation of the knob produces displacement of the coil 5. The channel 4;a1so carries a magnetic core I3 with a thread Ifi'locked in position by nuts I5. The core is only moved once, for initial adjustment of the core with reference to the coil. The winding '6 forms an inductance which may be connected with a fixed capacitance to form an oscillatory tunable circuit. The values of L and -C are chosen to resonate thecircuit at the desired frequency and the relative core movement produces the desired variation of L to cover the entire sub-range. In actual practice for the variation of L of the order of 2 a movement of will be required if the coil is.wound as a solenoid on the thin tubing off the same internal diameter. In the case, when two circuits are. simultaneously tuned the tube is extended in length so as to have adequate separation between the windings and the cores are fixed onthe rod I4. The pinion I0 engages a small rack I5 with a pointer I6 indicating on a portion of a suitable dial the position to which the-circuit is tuned. The dial may have printed on it call letters of the stations.

Figure 2 shows a modification of the tuning unit in which capacitors I6 and I1 consisting of two concentric cylinders is moved by a similar arrangement. The spring clutch I8 engaging cone I9 is used to engage the knob with tuning element. The coil 5 in this case is a self-supporting universal winding.

It is understood that the other tuning devices such as for instance short circuiting metal rings may be used instead of or with either magnet cores or condensers, as long as the general idea and arrangement of parts is carried out 1n the similar manner.

Figures 3 and 4 show the general tuner arrangements typical for the radio broadcast receiver application. Figure 3 shows the whole unit assembled around an eight section switch in which 5 positions are used for the broadcast tion of short wave stations.

One-single graduated dial 22 calibrated in frequencies maybe employed in the middle of the assembly, over which a transparent celluloid dial with call letters of those stations which may be conveniently heard in the given location may be superimposed to allow the operator a quick selecti-onof' five of those stations by the five upper knobs. When either of them is pushed in and once rotated to a desired station, it is left in the position for daily use. The whole assembly when mounted on a plate with associated coils, condensers, etc. comprise the whole tuning unit which for convenience may be moved within a reasonable distance from the chassis of the receiver, as it has a minimum number of outgoing connections. Additionalknobs actuating volume and tone controls may also be assembled on this control panel. For the convenience of the operator tobe able to quickly select desired stations in each sub-range, the knobs of each subrange, as well as the graduations, call letters, and pointers may be marked in difierent colors. Figure 1 shows that thepointers I6 are actuated by racks I5 engaged with pinions I0. Once such selections are made the call letter dial plainly indicates what stations are at the immediate disposal of the operator and to get any of these stations, he has only to press the corresponding knob.

7 It may also be convenient to dispose the sta tion selector on. two separate switches, having the ,dial 22 between the switches, in which case two l-section switches may be used as shown in Figure 4. A large .dial is employed, each horizontal line representing the calibrations of a part-range of which these upper ones may be broadcast ranges. In such an arrangement less confusion will arise as each knob is in line with its tuning range- The pointers may be actuated either by rack and pinion as previously described or by the usual system of pulleys and strings. It may be arranged in the known manner to illuminate only those parts of the dial which correspond tothe position of the operating knob.

It will be noted that the short wave portion of the dial is marked somewhat different from the previously described example. There, narrow rangesare employed: first 9.4 to 9.9 mc.; second 11.5 to 12'. mc., and third 14.5 to 15.5 me. which cover most of, usual stations, allowing better band spread and having certain electrical ad'- vantages, aslwill be later explained.

It is evident that in receivers covering a long wave band such as is used in European broadcasting, one or two extra sections should be added to complete the receiver.

The invention lends itself to the receiving circuits of the straight R. F. type or to superheterodyne receivers.

Figure 5 shows the electrical circuit of a two stage T. R. F. receiver embodying the invention and having 5 station selectors for broadcast range as above described. The circuit shows a high impedance choke 22 in the antenna circuit, coupled to the first circuit through a coupling condenser 23, first resonant circuit'capacity 24,

which may be of the order of IL/Lf, and ad-;

justable inductors 25, 26, and 21, Whose approximate minimum values are respectively 400, 200 and 100 h, with the maximum values of 880, 440 and 220 h. Such small range of variations enables one to use highly efficient small coils for better selectivity. Tube 29 is a radio frequency amplifier in the plate of which are connected tunable circuits of another set, similar to the first set and the pre-tuning of both circuits is done simultaneously and synchronously as already described. Tube 30 is the usual detector in the plate of which conventional audio circuits are represented by telephone 3 I. I

Figure 6 shows the application of the invention to the oscillator circuit of a superheterodyne receiver. An oscillator tube 32 is connected for v convenience as a Colpitts oscillator wherein capacitors 33 may be of 200 ,u tf each and the coils 25, 26, and 21 have minimum values approximately 150, 95, and 60 ch. Since a standard intermediate frequency of 455 kc. is employed the inductance variations required for tuning are reduced so that corresponding maximum values become approximately 250, 160, and 100 ph. It will be noted that since the low loss quality of the coil is relatively unimportant in the oscillator circuit very small coils not over maximum dimension may be employed for tuning. Cores made of magnetite mesh 70-140 may be employed for the broadcast range, while in the short wave region much finer magnetite dust, e. g. mesh 300 may be employed. The same considerations are applicable to short wave tuning except that the coils and condensers are of much smaller values, the coil being of the order of 11that the minimum.

While it is possible to use in the superheterodyne a preselector (antenna input circuit and R. F. stage, if employed) in accordance with the showings of the Figure 5, it is sometimes preferable to simplify the circuits and to reduce their cost' by the employment of a preselector constructed in accordance with Figure 7.

When the part-ranges are subdivided, substantially as previously described, it may become advantageous to tune the pre-selector to the wide band of frequencies of each part-range. With the above intermediate frequency part-ranges should be preferably smaller in frequency width, then the intermediate frequency to avoid station interference due to the 2nd harmonic. In this case as Figure 7 schematically represents, an input circuit of the band pass type is employed, having an antenna coupled inductively through a primary coil 34 to the coil 35 in parallel with which is a circuit capacitor 36 which may be of the order of 70 i for broadcast range. Coil 35 has three taps dividing the coil into three sections so that the total inductance of the coil varies in the above example from 200 to 600 h. The first circuit is tightly coupled, with the coupling coefficient of the order of 40%, by capacity 31 and mutual inductance between two coils, to another similar circuit 35, 35. Three switch points 28 correspond to three part-ranges. The output of the band pass filter is fed to a grid of the mixer tube or to an oscillator-converter tube. The arrangement of the coils of the filter is shown in Figure '7 where two windings 35 are so wound that the increase of inductance brings the necessary increase of mutual inductance. It is to be noted also that the antenna coil 34 is so placed as to produce increase of coupling with increase of inductance of coils 35. This arrangement of the preselector affords an increase of image ratio (ratio of direct signal to the second channel interference) as compared with single coil tunable inp-ut, but the cross-modulation from a neighboring strong station is somewhat increased, so that in special cases it may be advisable to employ an additional rejector circuit, tuned to the offending local station, in order to reduce its signal strength, such as shown on the figure, whereSB and 39 are respectively inductance and capacitance of the rejector circuit. A similar arrangement, but of different electrical quantities, may be employed for the reception of relatively broad short wave part-ranges, such as were set as one example of Figure 3. In that case, where narrow part-rangesare employed, such as in Figure 4 the preselector circuit will consist of a single circuit, tuned for the middle of each narrow band, the arrangement being substantially as was shown in one part of the band pass filter, by using tapped coils of appropriate value, the

free ends of the coil may be adjustable by magnetic type trimmers.

Should it be required to employ an additional R. F. tube for better sensitivity on the short wave, a second tapped coil may be employed, substantially as in the T. R. F. circuit of Figure 5, also tuned to a middle of each part-range, but it may be preferable to slightly stagger the resonance points of two coils in order to avoid attenuation towards the ends of the part range.

What I claim is:

l. A radio tuning device for instantaneous selection and presetting of the desired stations including'a plurality of adjustable circuits each tunable over a limited sub-range of a normal frequency spectrum, the circuit constants being so chosen as to cover said spectrum in steps, tuning means to vary the inductance of the circuits, electrical switching means to bring into operation the circuits corresponding to the desired range, a common operating member for said switching and said tuning means, said member being normally disconnected from the tuning means, and means responsive to a switching operation of said member to interconnect the latter to said tuning means.

2. A radio tuning device according to claim 1 in which a common dial having plurality of subranges for each set of circuits are employed, each circuit being provided with its own indicator within ,a sub-range.

3. In a superheterodyne receiver, having an input pre-selector circuit, an oscillator and an intermediate frequency channel a tuning device for an instantaneous selection and pre-setting of the desired station including a plurality of adjustable oscillator circuits, each independently and continuously tunable over a limited sub-range of the normal frequency spectrum tuningmeans to vary the inductance of said oscillator circuits, electrical switching means to bring into operation the circuits corresponding to the desired sub-range, a common operating member for said tuning and said switching means, and means responsive to a switching operation of said member to interconnect the latter to said tuning means.

WLADIMIR J POLYDOROFF. 

